Method for producing a continuous nitride layer

Abstract

Title: Method for producing a continuous nitride layer. The invention relates to a method for obtaining a layer made at least in part of a nitride (N), comprising firstly providing a stack comprising at least one set of pads (1000A1-1000B4) extending from a substrate (100). Each pad comprises at least one creep section (220A1-220A5) and a crystalline section (300A1, 300A5) overlying the creep section (200A1-200A5). A crystallite (510A1-510A5) is then grown by epitaxy on at least some of said pads until the crystallites coalesce to form a nitride layer (550A).The pads of the assembly are distributed on the substrate in such a way that their relative arrangement ensures that, during the epitaxy of the crystallites, the progressive coalescence of the crystallites always occurs between, on the one hand, a single crystallite or a plurality of coalesced crystallites, and on the other hand, an isolated crystallite. Figure for the abbreviation: Fig. 3H.

Description

Title of the invention: Method for producing a continuous nitride layer technical field

[0001] The present invention relates to the fabrication of continuous layers made of a nitride (N) preferably obtained from at least one of gallium (Ga), indium (In), and aluminum (Al). The invention finds application, for example, in the field of optoelectronic devices comprising a plurality of micrometer-sized light-emitting diodes (LEDs), generally called micro-LEDs. In this field, a particularly advantageous use of the invention relates to the fabrication of small screens generally called micro-displays. PRIOR TECHNOLOGY

[0002] For many microelectronic or optoelectronic applications, it is desirable to fabricate nitride layers from at least one of gallium, indium, and aluminum. Specific applications include, for example, the fabrication of micro-LEDs.

[0003] A nitride layer is classically obtained by epitaxial growth from a crystalline layer covering a plate.

[0004] A major challenge is to minimize the defect density in the nitride layer obtained by epitaxy. Indeed, the performance of microelectronic or optoelectronic devices made from these nitride layers is very sensitive to the density of structural defects such as dislocations.

[0005] These dislocations originate from the difference in lattice parameter between the epitaxial layer and the substrate, as well as the coalescence of small grains that are formed at the beginning of growth; these grains are slightly disoriented with respect to each other and they join together, forming structural defects at the coalescence joint, including dislocations, which can then cross the entire epitaxial structure.

[0006] The most direct way to solve these problems is to use substrates of the same nature as the layers to be epitaxially treated (homo-substrates). However, these substrates are not commercially available or are still only small in size, and are very expensive, which makes it impossible to cut substrates of sufficient size for the industrial applications envisaged.

[0007] The solutions considered to date for industrial applications are therefore based mainly on the use of hetero-substrates in combination with so-called "lateral growth" or ELOG methods, an acronym for "lateral epitaxial growth". "Overgrowth." This method, based on using a mask to block dislocations, reduces their density. However, these dislocations are distributed non-uniformly, which can cause problems during device fabrication.

[0008] Another solution consists of growing material epitaxially onto pre-existing patches of that material: this is the so-called pendeo-epitaxy process, which eliminates the need for growth on the mask. However, conventional pendeo-epitaxy solutions do not eliminate, or even significantly reduce, the appearance of defects generated by the coalescence of adjacent nuclei.

[0009] Patent application WO2019122461 describes a solution illustrated in Figures IA in 1D: a. A first step consists of providing a stack comprising a 200 fining layer, a 300 crystalline layer and a 500 nitride layer or 500 priming layer, typically a gallium nitride (GaN) layer. A 400 buffer layer may also be present between the fining layer and the 500 nitride layer. This step is illustrated in [Fig. 1A]. b. A second step consists of forming 1000A1-1000A4, 1000B1-1000B4 blocks by etching the crystalline layer 300, possibly the buffer layer 400, and at least a portion of the finishing layer 200 ([Fig. 1B]). Each block thus comprises a finishing segment 220A1-220A4, 220B1-220B4 from the finishing layer 200 and a crystalline segment 300A1-300A4, 300B1-300B4 from the crystalline layer 300. c. Grow crystallites 510A1-510A4, 510B1-510B4 on the 1000A1-1000A4, 1000B1-1000B4 plots by epitaxy until they coalesce (figures IC and 1D). The layer thus formed can continue to grow and thicken.

[0010] During their epitaxial growth, the crystallites formed at the top of the pads coalesce to form a continuous layer intended to form an optoelectronic or electronic device. During epitaxy, the portion of the pad formed by the fining section reaches (or exceeds) its glass transition temperature or a temperature very close to it. Under the stress of mechanical stress, this portion of the pad can deform ([Fig. 1E]). Thus, when two crystallites come into contact and coalesce, the mechanical stresses generated by this contact are transferred to the pads and therefore to the fining sections supporting them. The latter deform, thereby absorbing some of the mechanical stresses.This mobility of the plots due to the presence of the fining sections makes it possible in particular to accommodate relative misorientations of the crystallites with respect to each other, whether in the plane in which the substrate mainly extends ("twist") or out of plane ("tilt").

[0011] However, it appears that this method does not allow for obtaining satisfactory defect densities. As illustrated in Figures 2A and 2B, continuous layers obtained by such a process exhibit, in places, very high orientation angles of the material at the base of the nitride layer, indicating the existence of structural defects that are detrimental to the fabrication of devices from these continuous layers.

[0012] There is therefore a need to limit or even eliminate the drawbacks of known solutions. The present invention aims in particular to provide a solution to meet this need.

[0013] An objective of the present invention is to provide a solution for obtaining a nitride (N) layer made from at least one of gallium (Ga), indium (In), and aluminum (Al), exhibiting a significantly reduced defect density. SUMMARY

[0014] To achieve this objective, according to one embodiment, a process is provided for obtaining a layer made at least in part of a nitride (N) preferably obtained from at least one of gallium (Ga), indium (In) and aluminium (Al), comprising the following steps: a. provide a stack comprising at least one set of pads extending from a substrate, each pad comprising at least: i. a first section, called the fining section, formed in an amorphous material exhibiting a glass transition temperature. Glass transition? ü. a second, crystalline section, called the crystalline section, overlying the finage section, b. to grow by epitaxy a crystallite on at least some of said pads and to continue the epitaxial growth of the crystallites until coalescence of the crystallites carried by the pads of the set of pads, so as to form a nitride layer,

[0015] The process is characterized in that the studs of said set of studs are distributed on the substrate in such a way that the relative arrangement of the studs of the set of studs is such that during the epitaxy of the crystallites, the progressive coalescence of the crystallites always takes place between on the one hand a set, called a coalesced set, comprising a crystallite or a plurality of coalesced crystallites and on the other hand at least one crystallite, called an isolated crystallite, which has not already coalesced with other crystallites.

[0016] Thus, at a point of coalescence, the progressive coalescence of the crystallites always occurs between, on the one hand, a crystallite or a plurality of coalesced crystallites, and on the other hand, a single crystallite, which can also be described as an isolated crystallite since it has not previously coalesced with one or more other crystallites. The section of the slab underlying said isolated crystallite possesses all the mobility ne This is necessary to compensate for any misalignments and misorientations between the isolated crystallite and the coalesced crystallite or plurality of crystallites with which it coalesces. This prevents the formation of structural defects within the crystallites and therefore within the continuous layer during successive coalescences, ultimately resulting in a continuous layer of excellent quality.

[0017] Electronic and optoelectronic devices, for example LEDs or vertical devices such as vertical transistors or lateral components such as HEMT transistors, exhibiting very good performance can thus be fabricated from these layers having low densities of structural defects. BRIEF DESCRIPTION OF THE FIGURES

[0018] The aims, objects, features and advantages of the invention will become clearer from the detailed description of an embodiment thereof, which is illustrated by the following accompanying drawings in which:

[0019] [Fig.1A] Figures IA to 1E illustrate steps in a process for forming a continuous layer according to the prior art.

[0020] [Fig.1B]

[0021] [Fig.1C]

[0022] [Fig.1D]

[0023] [Fig.1E]

[0024] [Fig.2A] The [Fig.2A] is a photograph obtained by scanning electron microscopy (SEM) which illustrates continuous layers obtained by the process illustrated in figures IA to 1E.

[0025] [Fig.2B] Fig.2B is an image obtained by dark-field X-ray microscopy showing the orientation variations of the crystallites obtained by the process illustrated in Figures IA to 1E.

[0026] [Fig. 3A] Figures 3A to 3H illustrate steps of a process according to a non-limiting example of the process according to the present invention. [Fig. 3A] illustrates an example of stacking from which an example of the process according to the invention can be implemented.

[0027] [Fig.3B] The [Fig.3B] illustrates the stacking of the [Fig.3A] on which a priming layer is formed.

[0028] [Fig.3C] [Fig.3C] illustrates the result of a step consisting of forming a set of studs from the stacking of [Fig.3A] or of [Fig.3B].

[0029] [Fig.3D] The [Fig.3D] illustrates a phase of epitaxial growth of crystallites on the top of the studs, this growth phase not being completed.

[0030] [Fig.3E] Figures 3E to 3H illustrate the successive coalescences of the crystallites to form a continuous layer.

[0031] [Fig.3F]

[0032] [Fig.3G]

[0033] [Fig.3H]

[0034] [Fig. 4A] Figures 4A to 4F illustrate examples of stud arrangements enabling the fabrication of continuous layers with a low defect density. Figures 4A and 4B illustrate an example in which the studs are arranged in a logarithmic spiral.

[0035] [Fig.4B]

[0036] [Fig.4C] Fig.4C illustrates an example in which some of the plots are arranged along several parallel alignment axes.

[0037] [Fig.4D] Fig.4D illustrates an example in which the studs are arranged along an alignment axis.

[0038] [Fig.4E] Figures 4E and 4F illustrate an example in which the studs are arranged along five intersecting alignment axes.

[0039] [Fig.4F]

[0040] [Fig.5A] Figures 5A and 5B represent the coalescence of two continuous layers themselves previously formed by the coalescence of crystallites.

[0041] [Fig.5B]

[0042] The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. In particular, the relative thicknesses of the different layers, sections, crystallites and continuous layers are not representative of reality. DETAILED DESCRIPTION

[0043] Before proceeding with a detailed review of embodiments of the invention, optional features that may be used in combination or alternatively are listed below:

[0044] According to an advantageous embodiment, the pads carrying the crystallites forming the nitride layer are substantially arranged, in projection in a horizontal plane in which the upper face of the substrate extends mainly, in a logarithmic spiral.

[0045] According to one embodiment, the pads carrying the crystallites forming the continuous nitride layer are, in projection into a horizontal plane in which the upper face of the substrate extends mainly, substantially aligned along at least one axis called alignment.

[0046] According to one embodiment, the studs arranged on the same alignment axis are spaced at an increasing distance when traversing the alignment axis in a direction given from a given point, called the initial point.

[0047] According to one example, the pads bearing the crystallites forming the continuous layer are separated by a distance varying logarithmically from one to the next, said distance being measured along their alignment axis.

[0048] According to one example, the pads bearing the crystallites forming the continuous nitride layer are substantially aligned, in projection into a horizontal plane in which the upper face of the substrate extends mainly, along intersecting axes, the intersecting axes verifying a rotational symmetry with each other around a central point in projection into the horizontal plane.

[0049] According to one example, the plots are aligned along five intersecting axes.

[0050] According to one example, epitaxial growth is carried out at a temperature of tepitaxy, such as Tepitaxis > ki x with kj > 0.8.

[0051] According to one example, ki > 1, and preferably ki > 1.5.

[0052] Advantageously, the set of studs comprises at least 3 studs.

[0053] According to one embodiment, the stack comprises a plurality of sets of studs on the substrate, a continuous layer of nitride being formed from each set of studs, the epitaxial growth of the crystallites being interrupted before the crystallites belonging to two distinct sets of studs coalesce, so that the continuous layers formed from each set of studs are spaced apart from each other.

[0054] In this embodiment, in which several sets of pads allow the formation of several continuous layers that are separate from one another on the same plate, these different continuous layers are typically referred to as "vignettes." Each of these vignettes can then be used in the realization of an electronic or optoelectronic arrangement, such as an LED or micro-LED, or a vertical device such as a vertical transistor. The characteristics described below with reference to a set of pads, its crystallites, and the continuous layer formed from this set of pads apply mutatis mutandis to other sets of pads, the crystallites they carry, and the continuous layers formed by the coalescence of these crystallites.

[0055] According to one example, each plot has a top face and in which the growth by epitaxy of the crystallites takes place at least in part and preferably only from said top face.

[0056] According to one example, the method further comprises a formation step in the continuous layer of a device, the device being taken from among an LED and a transistor, for example a vertical transistor, for example a HEMT type transistor.

[0057] According to one embodiment, the studs of said set of studs are distributed on the substrate so that the relative arrangement of the studs of the set of studs is such that during the epitaxy of crystallites, at least at certain times the progressive coalescence of crystallites takes place between, on the one hand, the said coalesced set and, on the other hand, several isolated crystallites.

[0058] Alternatively, the dots of said set of dots are distributed on the substrate so that the relative arrangement of the dots of the set of dots is such that during the epitaxy of the crystallites, the progressive coalescence of the crystallites always takes place between, on the one hand, said coalesced set and, on the other hand, a single isolated crystallite.

[0059] According to one example, each plot has a section whose maximum dimension dpiot is between 10 and 500 nm (109 meters), the maximum dimension dpiot being measured in a plane parallel to a horizontal plane in which the upper face of the substrate extends mainly, preferably 20 nm < dpiot < 200 nm and preferably 50 nm < dpiot <100 nm.

[0060] According to a preferred example, the continuous layer has a section whose maximum dimension dlayer is between 0.5 and 10 qm (106 meters), the maximum dimension dlayer being measured in a plane parallel to a horizontal plane in which the upper face of the substrate extends mainly, preferably 0.8 qm < dlayer < 3 qm and preferably 1 qm < dlayer < 2 qm.

[0061] Preferably, the finishing layer is made of a material taken from: a. a silicon dioxide SixOy, where x and y are integers, and preferably the finishing layer is made of SiO2, b. a glass, c. a borosilicate glass, d. a borophosphosilicate glass (BPSG).

[0062] Advantageously, Tepitaxie < k2 x Tfusionmin, Tfusionmin being the lowest melting temperature among the melting temperatures of the sections forming the blocks, with k2 < 0.9 and preferably k2 < 0.8.

[0063] According to an advantageous embodiment, the pads comprise at least one buffer layer overlying the crystalline layer, and made of a material different from that of the continuous nitride layer, and preferably the continuous nitride layer is made of gallium nitride (GaN) and the buffer layer is made of aluminum nitride (Ain). This makes it possible to avoid the alteration phenomena of the GaN layer by reaction with the silicon layer, phenomena usually referred to as "melt-back etching".

[0064] According to one example, the plots include, before the epitaxial growth step of continuous nitride layers, at least one priming layer, surmounting said buffer layer and made of gallium nitride (GaN).

[0065] According to an advantageous example, providing said stacking includes providing a substrate elaborated of the silicon-on-insulator (SOI) type comprising a base substrate successively surmounted by an oxide layer forming said finishing layer and a semiconducting layer forming said crystalline layer.

[0066] According to an advantageous example, the finishing section has a height e22o such that c22o > 0.1xdpiot, dpiot being the diameter of the plot or more generally the edge-to-edge distance of the plot taken, at the level of the finishing section and in a direction parallel to a horizontal plane in which extends mainly a top face of the substrate, preferably e220 > lxdpiot.

[0067] According to one example, the step of forming the pads includes etching the crystalline layer and etching only a portion of the finishing layer so as to retain a portion of the finishing layer between the pads.

[0068] In the following description, the terms crystals and crystallites will be considered equivalent.

[0069] It is specified that, within the scope of the present invention, the terms "on," "overlies," "covers," or "underlying," or their equivalents, do not mean "in contact with." Thus, for example, "the deposition of a first layer on a second layer" does not necessarily mean that the two layers are directly in contact with each other, but rather that the first layer at least partially covers the second layer, either by being directly in contact with it or by being separated from it by at least one other layer or at least one other element, including air. Similarly, "a stud overlying a first layer" does not mean that the stud is necessarily in contact with that first layer, but rather that the stud is either in contact with that first layer or in contact with one or more layers arranged between the first layer and the stud.

[0070] The formation stages of the different layers and regions are understood in a broad sense: they can be carried out in several sub-stages which are not necessarily strictly successive.

[0071] In the following description, the thickness or height is taken along a direction perpendicular to the principal faces of the different layers. In the figures, the thickness or height is taken along the vertical or along the z-axis of the orthogonal coordinate system illustrated in figures IA to 1E, 3A to 3H and 5A and 5B.

[0072] Similarly, when it is indicated that an element is located opposite another element, this means that these two elements are both located on the same line perpendicular to the main plane of the substrate, i.e. on the same line oriented vertically (z-axis) in the figures.

[0073] A substrate, layer, or device "based" on a material M is understood to mean a substrate, layer, or device comprising only that material M or that material M and possibly other materials, for example, alloying elements. impurities or doping elements.

[0074] The terms "approximately", "about", "on the order of" mean "within 10%" or, when referring to an angular orientation, "within 10°". Thus, a direction substantially normal to a plane means a direction having an angle of 90+10° with respect to the plane.

[0075] The term "micro-LED" refers to an LED in which at least one dimension, measured in a plane parallel to the principal plane in which the substrate supporting the micro-LED extends (i.e., the XY plane of the orthogonal coordinate system referenced in the figures), is micrometric, that is, strictly less than 1 mm (10³ meters) and preferably less than or equal to 100 pm (1 pm = 10⁶ meters). Within the scope of the invention, the micro-LEDs, when projected onto a principal extension plane parallel to the principal faces of the micro-LEDs, i.e., parallel to a top face of the substrate, have maximum dimensions of micrometric size in the plane. Preferably, these maximum dimensions are less than a few hundred micrometers.

[0076] In the present invention, "vertical devices" means devices in which the load carriers move within the thickness of the layer, that is to say in a direction perpendicular to the planes in which the principal faces of this layer extend.

[0077] In the present invention, "HEMT" (High Electron Mobility Transistor) refers to field-effect transistors with high electron mobility, sometimes also called heterostructure field-effect transistors. Such a transistor comprises the superposition of two semiconductor layers having different band gaps that form a quantum well at their interface. Electrons are confined in this quantum well to form a two-dimensional electron gas. For reasons of high-voltage and high-temperature resistance, the materials of these transistors are chosen to exhibit a wide band gap.

[0078] An example of a method for forming a continuous layer according to the invention will now be described with reference to Figures 3A to 3H.

[0079] It should be noted that, according to one example, the process described below makes it possible to form a single continuous layer on a substrate 100 or on a wafer. According to another example, the process described below makes it possible to form a plurality of continuous layers on the same substrate 100 or on the same wafer. In the latter case, each layer is separate from the others and can be called a vignette. Each vignette can then be used to fabricate a device such as an LED or a micro-LED or any other vertical nitride-based device such as a HEMT transistor.

[0080] As illustrated in [Fig. 3A], a stacking is provided comprising at least one substrate 100, successively surmounted by a layer of finishing 200 and a crystalline layer 300. Thus the layer of finishing 200 is arranged between the substrate 100 and the crystalline layer 300.

[0081] According to one embodiment, the substrate 100 is silicon-based, amorphous or crystalline. It ensures the mechanical stability of the stack.

[0082] The crystalline layer 300 has a lower face 302 facing the finishing layer 200 and an upper face 301 whose function is to serve as a base layer for the epitaxial growth of the nitride of the continuous layer 550A that is ultimately desired. For example, the layer that is ultimately desired is a gallium nitride (GaN) layer. According to one embodiment, the crystalline layer 300 is based on single-crystal silicon. Alternatively, the crystalline layer 300 can be based on SiC or Al₂O₃.

[0083] Preferably, the finishing layer 200 is made of a viscous material. The finishing layer 200 has a glass transition temperature. It therefore exhibits a glass transition and displays the behavior of glass transition materials. Like all materials with a glass transition temperature, the finishing layer 200, under the effect of a temperature increase, deforms without breaking and does not return to its initial position after a temperature decrease. In contrast, the crystalline layer 300 does not naturally exhibit a glass transition. The crystalline layer 300 deforms, then disintegrates and can break. Consequently, the finishing layer 200 and the crystalline layer 300 are different. The finishing layer 200 is not crystalline.

[0084] The finage 200 layer is made of an amorphous material such as an oxide, preferably a silicon oxide SixOy, such as SiO2. The role of this layer will be explained later in the description.

[0085] Advantageously, but not limitingly, this stack comprising the substrate 100, the finishing layer 200, and the crystalline layer 300 constitutes a semiconductor-on-insulator substrate, preferably silicon-on-insulator (SOI). In this case, the finishing layer 200 is formed by the buried oxide layer (BOX) of the SOI substrate.

[0086] According to an advantageous embodiment illustrated in [Fig. 3A], a buffer layer 400 is deposited epitaxially on the upper face 301 of the crystalline layer 300. When the desired continuous layer 550A is made of GaN and the crystalline layer 300 is a silicon-based layer, this buffer layer 400 is typically made of aluminum nitride (AIN). This avoids the so-called "melt-back etching" phenomenon, generated by the very high reactivity between silicon and gallium at typical epitaxial temperatures (1000 / 1100°C), which leads to significant degradation of the continuous GaN layer 550A.

[0087] Typically, the thickness of the AIN layer is between 10 and 200 nanometers (109 meters).

[0088] As illustrated in [Fig. 3B], a priming layer 500 can also be deposited by epitaxy on the upper face 401 of the buffer layer 400. The function of this priming layer 500 is to facilitate the resumption of growth of the crystallites 510A1-510A5 during the subsequent steps. In this case, the epitaxial growth of the crystallites 510A1-510A5, illustrated in [Fig. 3D], occurs at least partially from an upper face of the priming layer 500. This priming layer 500 is preferably made of the same material as the continuous layer 550A that is ultimately desired. Typically, when the continuous layer material 550A is gallium nitride (GaN), the 500 seed layer is also GaN. This 500 seed layer typically has a thickness between 50 and 200 nanometers.

[0089] For the sake of brevity and clarity, only five pads 1000A1-1000A5 are shown in the figures to support a continuous 550A layer. Naturally, a continuous 550A layer can be formed on a greater number of pads. As will be described later, the number of pads and their period will be adjusted according to the desired size of the micro-LED.

[0090] It should be noted that the buffer layer 400 and the priming layer 500 are optional. Thus, according to embodiments not illustrated in Figures 3A to 3H, only the buffer layer 400 or only the priming layer 500 may be provided, or neither of these two layers 400 and 500.

[0091] As illustrated in [Fig. 3C], 1000A1-1000A5 blocks are then formed from the stack. These blocks are obtained by etching the stack into the finishing layer 200, with at least part of the etching extending into the finishing layer 200.

[0092] To form the pads by engraving, the numerous engraving techniques known to those skilled in the art may be used. In particular, conventional lithography techniques may be employed, such as photolithography techniques involving the formation of a mask, for example in resin, and then the transfer of the patterns from the mask into the stack. Electron beam lithography (e-beam) or nanometric printing techniques may also be used.

[0093] These 1000A1-1000A5 pads are small and can be described as nano-pads. Typically, the maximum dimension of the pad cross-section, taken in a plane parallel to the horizontal XY plane of the orthogonal XYZ coordinate system or to the plane of the upper face 101 of the substrate 100, and referred to as dpiot in [Fig. 3C], is between a few tens and a few hundred nanometers. More precisely, dpiot is between 10 and 500 nanometers, and preferably between 20 and 150 nm, and preferably between 50 and 100 nm, for example, on the order of 50 nm or 100 nm. If the pads have a circular cross-section, this maximum dimension dpiot corresponds to the diameter of the pads. If the pads have a hexagonal cross-section, this maximum dimension dpiot corresponds to the diagonal or the diameter of the circle passing through the corners of the hexagon. If these pads have a rectangular or square cross-section, this maximum dimension dpiot corresponds to the longest diagonal. It is understood that the cross-section of the pads may have a shape other than circular, hexagonal, rectangular, or square.

[0094] In the context of the present invention, the 1000A1-1000A5 plots are distributed in a particular way in projection in the XY plane: their arrangement is such that, as will be illustrated further on, the coalescences occurring successively during the implementation of the process involve on the one hand a single crystallite 510A1 (during the first coalescence which will be described later with reference to [Fig.3E]) or a plurality of already coalesced crystallites 510A1-510A4 (during the following coalescences, figures 3F to 3H), and on the other hand at least one isolated crystallite 510A2-510A5. In other words, the arrangement of plots 1000A1-1000A5 prevents any coalescence between, on the one hand, a first plurality of coalesced crystallites and, on the other hand, a second plurality of coalesced crystallites. To achieve this, plots 1000A1-1000A5 are not all equidistant from their nearest neighbors.The arrangement of the 1000A1-1000A5 plots must take into account the increase in projected dimensions in the XY plane of the 510A1-510A5 crystallites as they grow by epitaxy. Examples of the 1000A1-1000A5 plot arrangement will be given later with reference to Figures 4A to 4F.

[0095] As illustrated in [Fig. 3C], the pads are etched through the entire initiator layer 500, the entire buffer layer 400 (when present), and the entire crystalline layer 300. Preferably, only a portion 220 of the finishing layer 200 is etched. This embodiment has the advantage of preventing the nitride of the continuous layer 550A from growing on the finishing segments 220 during epitaxy. This epitaxial selectivity is particularly relevant when the continuous nitride layer 550A that is grown epitaxially is GaN and the finishing segments are SiO2. Conversely, if the finishing layer 200 is etched through its entire thickness using the same materials, then during epitaxy, the nitride of the continuous layer 550A develops from the upper face 101 of the substrate 100, which is usually made of silicon. This situation is obviously undesirable.

[0096] Furthermore, it has been observed that preserving an unengraved portion 210 of the The creep layer 200 facilitates the creep of the section 220, particularly when the crystallites are twist-oriented, i.e., in the principal planes of extension of the continuous layer 550A that we wish to obtain. These principal planes of extension of the continuous layer 550A are parallel to the horizontal XY plane of the XYZ coordinate system.

[0097] Preferably, the engraved thickness e22o, which forms the height of the creep section 220, is equal to half the thickness of the creep layer 200. This allows for very good reorientation of the crystallites during the formation of grain boundaries.

[0098] Fig. 3D illustrates the formation of 510A1-510A5 crystallites by epitaxial growth from the priming layer 500 (or from the top face 301 of the crystalline layer 300 when the layers 400 and 500 are absent).

[0099] As illustrated in this [Fig.3D], the 1000A1-1000A5 pads each support a 510A1-510A5 crystallite carried by a stack of 400A1-400A5, 300A1-300A5, 220A1-220A5 segments. The segments extend along the principal extension direction of the pad, i.e. vertically (Z) in Figures 3A to 3H.

[0100] The segments form circular cylinders if the cross-section of the studs is predominantly circular. If the cross-section of the studs 1000A1-1000A5 is polygonal, for example hexagonal, the segments then form cylinders with a hexagonal cross-section. Preferably, the segments are solid. The cross-section of the studs is taken parallel to the horizontal XY plane, that is, parallel to the planes in which the creep layer 220 and the crystalline layer 300 extend predominantly.

[0101] Regardless of the embodiment chosen, i.e., with or without a priming layer 500 and with or without a buffer layer 400, the epitaxial growth of the 510A1-510A5 crystallites occurs at least partially or entirely from the upper face 1001A1-1001A5 of the 1000A1-1000A5 block. Thus, this upper face 1001A1-1001A5 is formed either by the crystalline segment 300A1-300A5, or by the segment 500A1-500A5 formed by the priming layer 500, or by the segment 400A1-400A5 formed by the buffer layer 400. This makes it possible, in particular, to rapidly obtain 510A1-510A5 crystallites of significant thickness.

[0102] It will be noted that the upper faces 401, 501 of the buffer layer 400 and of the priming layer 500, that is to say the faces turned with regard to the continuous layer 550A which we wish to grow, have Gallium (Ga) type polarities, and not nitrogen (N), which considerably facilitates the obtaining of a high quality epitaxial nitride continuous layer 550A.

[0103] The growth of the 510A1-510A5 crystallites continues and extends laterally, particularly along planes parallel to the xy plane. The 510A1-510A5 crystallites grow until those borne by the two pads closest to each other of The other, labeled 1000A1 and 1000A2 in Figures 3C to 3H, are separated by a coalescent Pb distance ([Fig. 3E]). This coalescence occurs with few or no dislocations within the crystallites. It allows the formation of a continuous 500A layer from the 510A1 and 510A2 crystallites. This continuous 500A layer constitutes a coalesced unit.

[0104] The growth of the crystallites involved in this first coalescence 510A1, 510A2, as well as the other crystallites 510A3-510A5, continues until the continuous layer 500A formed by the crystallites 510A1 and 510A2 coalesces with the crystallite 510A3 carried by the nearest 1000A3 block. The 510A3 crystallite is thus added to the coalesced set. It should be noted that, due to the distribution of the 1000A1-1000A5 blocks on the substrate, from the beginning of its growth ([Fig. 3D]) until this stage of the process ([Fig. 3F]), the 510A3 crystallite, being coalesced with the continuous layer 550A, has never coalesced with another crystallite. Its plot 1000A3 therefore exhibits all the necessary mobility to accommodate misalignment in the XY plane or out of plane with the continuous layer 550A formed by the first two coalesced crystallites 510A1, 510A2. In [Fig.3F], a deformation of the 220A3 fining section according to its "tilt" angle is illustrated.A deformation of this 220A3 fining section, according to the "twist" angle, can occur alternately or simultaneously. The properties of this 220A3 fining section allow for a significant reduction of defects at the interface between the continuous 550A layer and the 510A3 crystallite. Explanations regarding the benefits of this precaution are provided later.

[0105] The continuous layer 500A is then formed by the crystallites 510A1, 510A2 and 510A3.

[0106] The growth of the continuous layer 500A continues, as does that of the as-yet-coalesced crystallites 510A4 and 510A5. A new coalescence occurs when the continuous layer 500A comes into contact with the crystallite 510A4 ([Fig. 3G]). The fining section 220A4 of the latter deforms so that the entire 1000A4 deforms and thus accommodates any misalignment and misorientation of the continuous layer 500A with the crystallite 510A4. The crystallites 510A4 and 510A5 are thus added to the coalesced whole.

[0107] Finally, [Fig.3H] illustrates a coalescence allowing the 510A5 crystallite to be integrated into the continuous 500A layer (i.e. into the coalesced whole).

[0108] As is clear from the figures, the continuous layer 550A extends at the end of the process between several pads 1000A1-1000A5 and forms a continuous layer.

[0109] It is understood that Figures 3A to 3H illustrate the example of a continuous layer 500A formed by adding a single crystallite 510 at each coalescence step, but that it is perfectly conceivable that several crystallites 510A1-510A5 coalesce simultaneously with the continuous layer 500A, provided that these are not themselves- even already coalesced with each other or with one or more other crystallites. Such an example will be described further with reference to [Fig.4F].

[0110] Figures 3A to 3H are not intended to provide a realistic visual representation of the deformation of the sprue sections. These figures aim to provide a schematic representation to facilitate understanding of the principle of crystallite coalescence without dislocation at the coalescence boundaries. In particular, the deformations of the sprue sections are not shown in all planes for the sake of brevity. Furthermore, the deformations of the blocks have been exaggerated for explanatory purposes. The upper surface of the continuous layer obtained at the end of the process has a much less rough, even smooth, appearance than that shown.

[0111] The growth of the 510A1-510A5 crystallites does not extend downwards. Moreover, this growth is selective in that it does not occur on the fining layer 200, which is typically made of an oxide. In this sense, the growth of the 510A1-510A5 crystallites occurs according to the principle of pendeo-epitaxy.

[0112] It should be noted that it is particularly advantageous to etch the 1000A1-1000A5 pads after the epitaxial formation of the buffer layer 400 and the initiator layer 500 (when these layers are present). Indeed, if one of these layers 400 or 500 were deposited after etching, it would form at least partially between the 1000A1-1000A5 pads on the upper surface of the finishing layer 200. In the case where the epitaxially treated nitride is GaN, and the finishing layer 200 is SiO2, then, at the epitaxial deposition temperature, the epitaxial growth of the continuous nitride layer 550A would not occur selectively but would, on the contrary, also take place between the 1000A1-1000A5 pads, which is naturally undesirable.

[0113] Most advantageously, the temperature at which the epitaxy is performed is higher than or on the order of the temperature of glass transition of the 200 fining layer. Thus, during epitaxy, the 220A1-220A5 fining sections are brought to a temperature which allows them to deform.

[0114] Consequently, if the 510A11-510A12 crystallites carried by two adjacent 1000A1-1000A2 patches are misoriented with respect to each other, during the coalescence of these two crystallites, the joint formed at their interface, usually referred to as a grain boundary or coalescence boundary, will form without dislocations to compensate for these misorientations. The deformation of the 220 grain segments thus makes it possible to compensate for these misorientations and to obtain a continuous 550A layer with little or no dislocations at the coalescence boundaries.

[0115] We denote by dcouche the maximum dimension of a continuous layer measured parallel to the xy plane. Thus, dcouche corresponds to the maximum dimension of a projection of the continuous layer onto a plane parallel to the xy plane. Preferably 0.8 pm < dcouche < 3 pm and preferably 1 pm < dcouche < 2 pm. dcouche depends on the speed and duration of epitaxial growth as well as the number and size of the spots.

[0116] The distances (for example, referenced Pb P2, P3, P4... in the figures) separating two pads whose overlying crystallites are successively coalesced with the continuous layer are typically greater than 300 nm, and for example, between 300 nm and 10 pm, or for example, between 300 nm and 5 pm. These distances can be chosen, in particular, according to the size of the component to be manufactured from the continuous layer formed at the end of the process. The increase in the distance between pads as pads with increasingly higher refractive indices are considered typically occurs more rapidly for a small component than for a large component. Indeed, for a large component, the pads could then be very far apart. However, achieving coalescence of crystallites belonging to very distant plots can be complex, particularly because at an advanced stage of the process, the continuous layer is quite thick.It should be noted, however, that a significant thickness of the continuous layer may be desirable for the fabrication of certain devices, for example for power electronics. Therefore, coalescence between crystallites and the continuous layer is possible when the nitride thickness is substantial (potentially up to several tens of micrometers).

[0117] The process for fabricating the continuous 550A layer can be stopped at the end of [Fig. 3H]. Alternatively, this process can be continued to form a micro-LED from the continuous 550A layer.

[0118] According to a non-limiting embodiment not shown, quantum wells are created within the continuous 550A layer. This embodiment advantageously allows for the direct fabrication of a micro-LED with a size corresponding to the initial size of the continuous layer. To fabricate quantum wells within the continuous 550A layer, those skilled in the art can implement known prior art solutions. Thus, once the 510A1-510A5 crystallites have coalesced, the same growth conditions are adopted for the wells as in conventional two-dimensional growth.

[0119] The smallest possible dimension for micro-LEDs depends on the ultimate resolution of the chosen structuring methods: for example, for arrays of dots fabricated by nanoimprinting, dot sizes of 50 nm and distances between dots of 100 to 150 nm are achieved. This means that continuous layer dimensions of 1 to 2 pm are obtained. This is therefore on the order of the pixel sizes sought for high-resolution p-displays.

[0120] Explanation of the principle of coalescence without dislocation or with few dislocations) within continuous layers

[0121] As indicated above with reference to figures 3E to 3H, the formation of the continuous layer 500A proceeds through the successive coalescences of isolated 510A1-510A5 crystallites.

[0122] As illustrated in Figures 5A and 5B, the coalescence of sets of already coalesced crystallites induces defects at the coalescence joints.

[0123] Figures 5A and 5B illustrate the example of two continuous layers 500A', 500B' each having been obtained by coalescence of two crystallites (510A1' and 510A2' on the one hand, 510B1' and 510B2' on the other hand), each supported by a pad (1000A1' and 1000A2' on the one hand, 1000B1' and 1000B2' on the other hand). The crystal planes of these two layers exhibit an angular orientation defect identified by the angle [3.

[0124] One might expect that, as in the case of the coalescence of two isolated crystallites, this orientation defect would be compensated by the properties of the fining sections of each of the pellets. It has been observed, however, that compensation does not occur, or at least occurs to an insufficient extent to satisfactorily limit the coalescence defects.

[0125] This can be explained by the following. During the initial coalescence of a crystallite with a neighboring crystallite, the underlying fining section deforms according to the relative misorientations of these first two crystallites. After this initial coalescence, the fining section is therefore mechanically constrained in a direction dependent on these misorientations.

[0126] If a new coalescence occurs, two cases can then be distinguished: a. The coalescence of the continuous layer occurs with an isolated crystallite (a crystallite that has not yet coalesced with one or more other crystallites is called an isolated or single crystallite): the slab section underlying this isolated crystallite exhibits considerable mechanical freedom and can, on its own, compensate for the misorientations between the crystal lattices of the continuous layer and the isolated crystallite. It is understood that deformation of the slab sections underlying the continuous layer is also possible, but to a much lesser extent than the deformation of the slab section underlying the isolated crystallite. b. The coalescence of the continuous layer occurs with another continuous layer, also obtained by the coalescence of crystallites carried by several pads (case illustrated in [Fig. 5B]): the different fining sections are then excessively constrained due to their mechanical dependence on the continuous layer and the other fining sections. Their presence does not compensate for the misalignments between the two continuous layers, and the coalescing layers cause numerous defects within the crystallites, particularly at the coalescence joint. It is understood that the underlying fining sections the two continuous layers can deform, but to an extent too small to compensate on their own for the misorientations of the continuous layers.

[0127] In other words, the fining sections of the plots 1000A1', 1000A2', 1000B1', 1000B2' supporting the crystallites involved 510A1', 510A2', 510B1', 510B2' in a coalescence between already coalesced crystallites exhibit much lower mobility than when each of them supports an isolated crystallite. It is this difference in mobility that explains why the principle of coalescence of raw crystallites by pendeo-epitaxy does not apply satisfactorily to a network of plots with arbitrary relative arrangements.

[0128] Figures 5A and 5B illustrate the fact that an out-of-plane misalignment of the continuous layers 500A', 500B' is not compensated by the presence of the fining sections, but it is understood that the same observation can be made for a misalignment in the xy plane.

[0129] As explained above, it has been observed that if an isolated crystallite is involved in coalescence, its fining section alone compensates for its misalignments with the continuous layer. Thus, the invention proposes to arrange the pads on the surface of the substrate in such a way that only this situation is encountered during the progressive formation of the continuous layer, and that the coalescence of two continuous layers, each originating from several crystallites, is avoided. Thus, according to the invention, at a point of coalescence, the progressive coalescence of the 510A1-510A5 crystallites always occurs between, on the one hand, a single 510A1 crystallite or a plurality of coalesced 510A1-510A4 crystallites, and on the other hand, an isolated 510A2-510A5 crystallite.This avoids the formation of structural defects within the crystallites and therefore of the continuous layer during successive coalescences, ultimately resulting in a continuous layer of excellent quality.

[0130] As previously stated, this does not preclude several coalescences from occurring simultaneously at the level of the set of plots. In this case, a plurality of crystallites that have already coalesced can coalesce simultaneously with a plurality of crystallites isolated from each other, that is, having not previously coalesced with any other crystallite.

[0131] It is understood that two crystallites forming part of the continuous layer created by successive coalescences are considered to be coalesced with each other, whether or not they were in direct contact with each other during the coalescence of one of them into the continuous layer. Generally, any crystallite in the continuous layer is considered to be coalesced with all the other crystallites forming the continuous layer, from the moment of its integration by coalescence into the continuous layer. The continuous layer forms, in fact, a coalesced whole within which the boundaries between crystallites cannot be truly defined, particularly as the epitaxy progresses. Thus, the coalescence The progressive coalescence of crystallites, which is controlled during the process according to the invention, is understood as the successive addition of one or more crystallites to the continuous layer. In particular, it is entirely possible that during the process according to the invention, two crystallites forming part of the continuous layer may come into contact and coalesce again, this time directly. These coalescences can be referred to as internal coalescences. Internal coalescences are not relevant to the progressive coalescence of crystallites, since during an internal coalescence, no new crystallite is added to the continuous layer. As will be discussed later, precautions regarding the arrangement of the pads can be taken to optimize these internal coalescences.

[0132] It should be noted that a variation in growth rate may occur during the process due to unavoidable variations in the process (for example, due to the injection of precursors, variations in temperature or pressure, etc.). Advantageously, it is provided that varying the distance between pellets from a center of symmetry of the coalescence compensates for this variation in the coalescence rate for the same set of pellets. In this way, even under the effect of a variation in the coalescence rate, the principle of formation of the continuous layer by successive coalescences of isolated crystallites is verified.

[0133] Examples of plot arrangement allowing coalescence without dislocation or with few dislocations) within continuous layers

[0134] Various examples of the arrangement of the studs on the substrate 100 allowing to obtain a continuous layer having a low density of defects will now be described with reference to figures 4A to 4F.

[0135] It is understood that the arrangement of the plots is understood as their distribution in space in projection in the xy plane, and particularly in projection on the upper face 101 of the substrate 100.

[0136] The distance between two neighbouring plots is measured from one edge of one of these two plots to one edge of the other of these two plots, in projection in the xy plane, as illustrated in [Fig.3C].

[0137] A first example of the arrangement of the 1000A1-1000A5 pads on the substrate 100 is illustrated in Figures 4A and 4B. In this example, the 1000A1-1000A5 pads are arranged in a logarithmic spiral. Such a spiral is a curve whose polar equation is of the form r = abü, with a and b positive real numbers and r the radius measured between the center of the spiral and the point on the curve forming an angle θ with an arbitrary origin axis in the horizontal XY plane. Advantageously, therefore, the 1000A1-1000A5 pads are arranged on a theoretical curve of this shape. The distribution of the 1000A1-1000A5 pads on this theoretical curve is chosen, in particular, according to the level of control of the processes involved, especially the process of epitaxy, and their variability. The better the control, the more the spacing between two consecutive plots on the curve can increase slightly as one travels the curve from the origin.

[0138] Fig. 4A illustrates a theoretical arrangement following such a model, while Fig. 4B is a top view SEM photograph of blocks arranged according to this embodiment.

[0139] This embodiment is particularly advantageous because it allows for a high density of spots on the substrate surface, resulting in rapid coalescence of the crystallites. Indeed, with identical epitaxial growth parameters, the greater the density of spots, the higher the coalescence rate. The density of spots on the substrate surface is defined, projected onto the horizontal XY plane, as the ratio between the area occupied by the spots on the upper face 101 of the substrate 100 and the area of ​​this upper face 101 of the substrate 100.

[0140] According to another embodiment illustrated in [Fig. 4D], the plots are aligned along a single axis, called the alignment axis. A direction of alignment is defined for this alignment axis, as well as an initial point positioned on this same axis. A first plot 1000A1 is located on this alignment axis, for example, at the initial point. The other plots are also located on this alignment axis, and the distance separating two consecutive plots 1000A1-1000A6 increases as one moves along the alignment axis in the direction of alignment. Denoting Pb P2, P3, P4, and P5 as the distances separating, respectively, the first 1000A1 and the second 1000A2 plots, the second 1000A2 and the third 1000A3 plots, the third 1000A3 and the fourth 1000A4 plots, the fourth 1000A4 and the fifth 1000A5 plots, and finally the fifth 1000A5 and the sixth 1000A6 plots, the order of the plots being given according to the direction of alignment, we thus have: Pi <P2<P3<P4<P5.Denoting i as the index of the plot on the alignment axis, with i ranging from 1 to N, N being the number of plots arranged along the alignment axis, we preferably have, for i>2, Pi>l,l*Pi b Advantageously, the distance between plots evolves, on the alignment axis and according to the direction of alignment, according to a geometric sequence: for i>l, Pi=aqi, a and q being positive real numbers, with preferably 2 < q and / or q > 1,1. .

[0141] This embodiment can be described as an "online" arrangement.

[0142] According to another embodiment illustrated in [Fig. 4C], some of the studs are arranged along alignment axes as defined previously with reference to [Fig. 4D]. These alignment axes are parallel to each other. To allow for good initiation of coalescence at the beginning of the process, it is also planned that other pads will not necessarily be aligned on one of the alignment axes.

[0143] The studs can, for example, be arranged along axes parallel to each other and perpendicular to the alignment axes mentioned above. These axes are designated as secondary alignment axes. Studs arranged on the same axis Secondary alignment points are preferably arranged at a constant pitch. Furthermore, considering all secondary alignment axes in the direction parallel to all alignment axes and in the same alignment direction as these axes, the pitch between points aligned on the same secondary alignment axis increases. In this example, care is taken to ensure that the distance separating two successive alignment axes (which can also be seen as the pitch between points on the secondary alignment axes) is always greater than the pitch between points aligned along the alignment axes. This example is illustrated in [Fig. 4C].

[0144] According to an embodiment illustrated in Figures 4E and 4F, the markers are arranged along a plurality of intersecting alignment axes, for example five as shown. A central point can be defined, at which a marker may or may not be located, corresponding to the point of intersection of these alignment axes. The markers are then distributed along branches, each originating from the central point.

[0145] Advantageously, and as is highlighted in [Fig.4F], the plots are distributed over concentric circles.

[0146] On each of the branches, the pads can be arranged as described for a single alignment axis, the initial point of the alignment axis as defined in the previous embodiment then being the point of intersection of the alignment axes defined here.

[0147] This embodiment can be described as a “star” arrangement.

[0148] Figure 4F highlights the coalescence order of crystallites in an example of this embodiment. It is a top view of a set of patches at different stages of epitaxial crystallite growth. The patches are represented by the black dots. The different concentric disks around a single patch correspond to different stages of growth of the crystallite supported by that patch. More precisely, a disk corresponds to a stage of growth at which a coalescence (or several simultaneous coalescences) occurs. This figure takes into account internal coalescences as defined above.

[0149] In this example, a first plot 1000A1 is located at the central point of the set of plots, and five second plots 1000A2 are located on a first circle centered on the central point of the set of plots. A first growth phase takes place and ends with the coalescence of the first plot 1000A1 with the five second plots 1000A2 (these five coalescences occurring substantially simultaneously). This coalescence forms a continuous layer.

[0150] It should be noted that during the first growth phase, the distance between the second pads 1000A2 and the third pads 1000A3 (and, more generally, any other pad of higher value) is sufficiently large for their crystallites to The prospects do not coalesce at this stage of the process (i.e., P2>Pi). This ensures that the crystallites supported by the second 1000A2 pads are indeed isolated crystallites upon coalescence with the first 1000A1 pad.

[0151] During a second growth phase, all the crystallites continue to grow until the continuous layer coalesces with the crystallites supported by the third 1000A3 pads (here, five in number). It should be noted again that during the second growth phase, the distance between the third 1000A3 pads and the fourth 1000A4 pads (and, more generally, any other higher pad) is sufficiently large so that their respective crystallites do not coalesce at this stage of the process (i.e., P3>P2). This ensures that the crystallites supported by the third 1000A3 pads are indeed isolated crystallites when they coalesce with the continuous layer.

[0152] The same observations can then be made for the coalescence of the third plots 1000A3 on the one hand and the fourth plots 1000A4 on the other hand, respectively during a third and a fourth phase of growth.

[0153] It is understood that the different phases of epitaxial growth typically proceed continuously and are represented and described separately here for explanatory purposes only. In particular, the concentric circles are merely schematic representations of the progress of growth at different points in the process but have no physical reality at the end of the process.

[0154] The various examples of the arrangement of the 1000A1-1000A5 pads on the substrate 100 described above made it possible to obtain continuous layers of very high quality, greatly reducing the defect density compared to layers obtained without regard to the pad arrangement. In particular, the rotational symmetry allowed by the distribution of the pads around the first pad 1000A1 makes it possible to limit or even eliminate potential defects caused by internal coalescence in the continuous layer. It also facilitates the fabrication of the pads.

[0155] It is understood, however, that any arrangement of the pads allowing the formation of a continuous layer solely by adding isolated crystallites to a cluster of crystallites (or possibly, at the beginning of the process, to another isolated crystallite) will yield equally satisfactory results. For example, removing the central pad is a possibility.

[0156] The non-limiting example described above refers to the use of the nitride layer to form an LED or a micro-LED. As stated previously, this example is not limiting. The described method can equally be used to fabricate other nitride-based devices, for example, vertical devices such as HEMT transistors.

[0157] The invention is not limited to the embodiments described above and extends to all embodiments covered by the invention.

Claims

Claims

1. A method of obtaining a layer made at least in part of a nitride (N) preferably obtained from at least one of gallium (Ga), indium (In) and aluminum (Al), the method comprising the following steps: • provide a stack comprising at least one set of pads (1000A1-1000B4) extending from a substrate (100), each pad (1000A1-1000B4) comprising at least: i. a first section, called the finishing section (220A1-220A5), formed in an amorphous material having a glass transition temperature ii. a second, crystalline section, called the crystalline section (300A1-300A5), surmounting the finishing section (200A1-200A5), • growing by epitaxy a crystallite (510A1-510A5) on at least some of said pads (1000A1-1000A5) and continuing the epitaxial growth of the crystallites (510A1-510A5) until coalescence of the crystallites (510A1-510A5) carried by the pads (1000A1-1000A5) of the set of pads, so as to form a continuous layer (550A) of nitride, the method being characterized in that the pads (1000A1-1000A5) of said set of pads are distributed on the substrate (100) so that the relative arrangement of the pads of the set of pads is such that during the epitaxy of the crystallites (510A1-510A5), the progressive coalescence of the crystallites (510A1-510A5) always takes place between on the one hand a set, called a coalesced set, comprising a crystallite (510A1) or a plurality of crystallites (510A1-510A4) coalesced and on the other hand at least one crystallite, called an isolated crystallite (510A2-510A5), which has not already coalesced with other crystallites.

2. Method according to the preceding claim, in which the pads (1000A1-1000A5) carrying the crystallites forming the continuous layer (550A) of nitride are substantially arranged, in projection in a horizontal plane (XY) in which the upper face (101) of the substrate (100) mainly extends, according to a logarithmic spiral.

3. Method according to claim 1, in which the pads (1000A1-1000A5) carrying the crystallites forming the continuous layer (550A) of nitride are, in projection in a horizontal plane (XY) in which the upper face (101) of the substrate (100) mainly extends, substantially aligned along at least one so-called alignment axis.

4. Method according to the preceding claim, in which the pads (1000A1-1000A5) arranged on the same alignment axis are spaced apart by an increasing distance while traveling along the alignment axis in a given direction from a given point, called the initial point.

5. Method according to any one of the two preceding claims, in which the pads (1000A1-1000A5) carrying the crystallites forming the continuous layer (550A) are separated by a distance varying logarithmically from near to near, said distance being measured along their alignment axis.

6. Method according to claim 1, in which the pads (1000A1-1000A5) carrying the crystallites forming the continuous layer (550A) of nitride are substantially aligned, in projection in a horizontal plane (XY) in which the upper face (101) of the substrate (100) mainly extends, along concurrent axes, the concurrent axes verifying between them a rotational symmetry around a central point in projection in the horizontal plane (XY).

7. Method according to the preceding claim, in which the pads (1000A1-1000A5) are aligned along five concurrent axes.

8. A method according to any one of the preceding claims wherein the epitaxial growth is carried out at a temperature Tepitaxy, such that Tepitaxy > ki x TtransiPonvitreuse, with k| > 0.

8.

9. Method according to the preceding claim, in which ki > 1, and preferably ki > 1.

5.

10. A method according to any preceding claim wherein the set of pads comprises at least 3 pads.

11. A method according to any preceding claim wherein the stack comprises a plurality of sets of pads on the substrate, a continuous layer of nitride being formed from each set of pads, the epitaxial growth of the crystallites being interrupted before the crystallites belonging to two distinct sets of pads coalesce, so that the continuous layers formed from each set of pads are spaced apart from each other.

12. Method according to any one of the preceding claims, in which each pad (1000A1-1000A5) has an upper face (1001A1) and in which the epitaxial growth of the crystallites (510A1-510A5) is carried out at least in part and preferably only from said upper face (1001A1).

13. A method according to any preceding claim further comprising a step of forming in the continuous layer (550A) a device, the device being taken from an LED and a transistor, for example a vertical transistor, for example a HEMT type transistor.

14. Method according to any one of the preceding claims in which the pads (1000A1-1000A5) of said set of pads are distributed on the substrate (100) so that the relative arrangement of the pads of the set of pads is such that during the epitaxy of the crystallites (510A1-510A5), at least at certain times the progressive coalescence of the crystallites (510A1-510A5) takes place between on the one hand said coalesced set and on the other hand several isolated crystallites (510A2-510A5).

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